Hitchcocks Forum

I will shortly be fitting a set of high-capacity oil pumps from our host and would welcome any tips for the fitting and lapping process. I have bought the lapping tool. Would I be right in thinking that FINE valve grinding paste would be too coarse, even for the first stage of lapping? And what's the best stuff to use as lapping paste? I have T-Cut, Brasso and good old Solvol Autosol - do I need anything else? Thanks!

A timely question for me, because I'm about to fit a new pump spindle and high capacity pumps to my engine. There is some info in our host's technical notes, and I found a brief reference in the Snidal manual which mentions that fine grinding paste can be used (and must be thoroughly cleaned out afterwards!)
I suppose it depends on the extent of any scoring in the housing in the timing cover. I assume that the objective is a smooth surface for the pump disc to work against.
I'm going to try Autosol first. I await some more replies from others who have done the job!

Have you a copy of the workshop manual? It's online at http://fixmybull.com/ if you haven't.

Unless the face is very worn you should be OK with Solvol and it is less likely to cause any problems if a trace remains, you will soon see if the faces are level and if not then use fine grinding paste.

Thanks Another Allan - for the link to the service manual. Never seen it before - that'll come in very handy!

And thanks Dennis!

How essential do we think lapping in these pumps is? The pumps will pressure relieve on the spring, so if the fit isn't perfect, then it will relieve a little less and will bed in very gently over time.

Or, if the housing is scored, they may not send enough oil up to the top end........

Yes, if the surface is damaged, but if there is no scoring? I'll bet that when the bikes are made they don't lap them in. Whereas inlet/exhaust valves would be lapped because that needs to be gas tight.

One action of the pump is piston pressure, then the other is the piston retracting where lapping might have only a small effect. I don't know, but just thinking about it.

There is some talk that the oil pump spindles can fail because a big-end is too snug. That would imply that either there is no pressure relief or the pump is working too well (or both).....? I have just done my big-end and the big-end is as snug as I felt reasonable. I didn't lap as surfaces looked ok and oil flow looks good.

Why does anyone fit higher delivery pumps to a slow reving ,low hp engine ? I can't see any gain ,only possible pump spindle wear when the oil is cold.The big end oiling does not rely on quantity only continuity.